1. Field of the Invention
The present invention relates to a feed forward controlling circuit and method, and more particularly to a feed forward controlling circuit and method for voltage ripple restraint.
2. Description of Related Art
Generally, mains power provided by a power company is AC (Alternating Current) power, but many electronic devices have to use DC (Direct Current) power. Therefore, the AC power is required to be converted into DC power for the electronic devices to use.
However, during the process for converting the AC power to the DC power, some of the AC portion cannot be completely removed from the DC power and the AC portion, which is not eliminated, will generate ripples.
Accordingly, the conventional technique provides a power supply for ripple restraint. With reference to FIG. 14, the power supply includes a rectifier 41, a power factor controller (PFC) 42, a power converter 43, a feedback circuit 44, a controller 45, a ripple detecting module 46, a communicating module 47, and a compensation processing module 48.
The rectifier 41 is electrically connected with an AC power source 50 and receives an AC power from the AC power source 50. The rectifier 41 converts the AC power into a DC power and outputs the DC power. The power factor controller 42 is electrically connected with the rectifier 41 and the power converter 43, and receives the DC power. The power factor controller 42 corrects power factor of the DC power and outputs the DC power to the power converter 43. The power converter 43 is electrically connected to the controller 45 and receives a control signal generated by the controller 45. The power converter 43 includes a power output terminal to output an output voltage Vout.
The feedback circuit 44 is electrically connected with the output terminal of the power converter 43 to detect the output voltage Vout. The feedback circuit 44 generates a feedback signal in accordance with the output voltage Vout and outputs the feedback signal to the controller 45. The controller 45 adjusts the control signal in accordance with the feedback signal to stabilize the output voltage Vout.
The ripple detecting module 46 is electrically connected with an input terminal of the power converter 43 to detect ripple in the DC power which is corrected by the PFC 42. The communication module 47 is electrically connected with the ripple detecting module 46 to receive the ripple detected by the ripple detecting module 46 and transmits the ripple to the compensation processing module 48. The compensation module 48 generates a compensation signal in accordance with the ripple, and outputs the compensation signal to the output terminal of the power converter 43 so as to compensate the power voltage Vout from the output terminal of the power converter 43 and reduce the ripple in the power voltage Vout.
However, the input terminal and the output terminal of the power converter 43 are respectively a primary side and a secondary side of the power converter 34. The primary side and the secondary side are separated from each other. Therefore, when the aforementioned method is used to reduce the ripple, the ripple signal detected at the primary side of the power converter 34 is processed first and then the ripple signal is transmitted to the secondary side of the power converter 45 via the communication module 47 so as to compensate the output voltage Vout. Accordingly, the circuit design is extremely difficult and it is necessary to improve the conventional manner to reduce the ripple.